In recent years, cooling of the combustion chamber has become the most important task as the combustion pressure of a liquid-propellant rocket engine has increased.
Heretofore, a combustion chamber has been manufactured by bundling several hundred tubes as shown in FIG. 1B of the accompanying drawings which is an enlarged view of the interior of the dotted circle of FIG. 1A. However, such a tube structure is inferior in cooling performance and cannot be adopted in a high combustion pressure engine for large heat load.
For this reason, a combustion chamber having a grooved cooling wall as shown in FIG. 2 of the accompanying drawings has been developed. This grooved cooling wall has a dual merit that the area of the inner surface 1 of the combustion chamber which is in contact with hot combustion gases is small as compared with the tube structure of FIG. 1B while, on the other hand, the area of cooling passages 2, namely, the cooling area, is large, and thus it is a very advantageous structure for an engine of high combustion pressure.
However, the manufacture of such grooved rocket combustion chamber has suffered from numerous problems. That is, in the method of manufacture according to the prior art, grooves 5 extending axially on the combustion chamber as shown in FIG. 3B of the accompanying drawings are formed in an inner cylinder 4 made of copper or a copper alloy as a metal of good heat conductivity as shown in FIG. 3A of the accompanying drawings, by machine work. Subsequently, an outer cylinder 6 is attached to the outer side of the grooved portion in a manner as shown in FIG. 3C of the accompanying drawings and in that case, the inner cylinder 4 and the outer cylinder 6 must be rigidly joined together without the cooling grooves 5 being adversely affected.
The brazing method and the electroforming (electrolytic deposition) method are known as such joining method. However, in the brazing method, the brazing material flows into the cooling grooves 5 to vary the cross-sectional area of the grooves, and this makes it difficult to obtain a predetermined cooling effect and may in most cases lead to the burning of the engine. Also, it is nearly impossible to accomplish brazing uniformly over the entire engine.
On the other hand, the electroforming method is a method of forming an outer cylinder 6 outside the inner cylinder 4 by electroplating and, for instance, used in the manufacture of an engine for a space shuttle. However, the outer cylinder formed by this method readily permits internal stress to be created therein and thus is weak in strength. To suppress such internal stress, it is necessary to delay the electrolysis reaction and a reaction time as long as several hundred to several thousand hours is required for making an outer cylinder of a predetermined thickness. Moreover, the outer cylinder 6 thus manufactured is made of Ni and is therefore poor in ductility, and it is known that the stress created in the engine concentrates in the inner cylinder 4 of Cu, thereby reducing the life of the engine.